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🔗 Spaceflight 🔗 Physics 🔗 Alternative Views 🔗 Physics/relativity

The Alcubierre drive, Alcubierre warp drive, or Alcubierre metric (referring to metric tensor) is a speculative idea based on a solution of Einstein's field equations in general relativity as proposed by Mexican theoretical physicist Miguel Alcubierre, by which a spacecraft could achieve apparent faster-than-light travel if a configurable energy-density field lower than that of vacuum (that is, negative mass) could be created.

Rather than exceeding the speed of light within a local reference frame, a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel. Objects cannot accelerate to the speed of light within normal spacetime; instead, the Alcubierre drive shifts space around an object so that the object would arrive at its destination faster than light would in normal space without breaking any physical laws.

Although the metric proposed by Alcubierre is consistent with the Einstein field equations, construction of such a drive is not necessarily possible. The proposed mechanism of the Alcubierre drive implies a negative energy density and therefore requires exotic matter. So if exotic matter with the correct properties cannot exist, then the drive could not be constructed. At the close of his original article, however, Alcubierre argued (following an argument developed by physicists analyzing traversable wormholes) that the Casimir vacuum between parallel plates could fulfill the negative-energy requirement for the Alcubierre drive.

Another possible issue is that, although the Alcubierre metric is consistent with Einstein's equations, general relativity does not incorporate quantum mechanics. Some physicists have presented arguments to suggest that a theory of quantum gravity (which would incorporate both theories) would eliminate those solutions in general relativity that allow for backwards time travel (see the chronology protection conjecture) and thus make the Alcubierre drive invalid.

🔗 Computing 🔗 Lists 🔗 Java

This article provides non-exhaustive lists of Java SE Java virtual machines (JVMs). It does not include a large number of Java ME vendors. Note that Java EE runs on the standard Java SE JVM but that some vendors specialize in providing a modified JVM optimized for Java EE applications. A large amount of Java development work takes place on Windows, Solaris, Linux and FreeBSD, primarily with the Oracle JVMs. Note the further complication of different 32-bit/64-bit varieties.

The primary reference Java VM implementation is HotSpot, produced by Oracle Corporation.

🔗 Skepticism 🔗 Zimbabwe 🔗 Paranormal 🔗 Folklore

On September 16, 1994, there was a UFO sighting outside Ruwa, Zimbabwe. 62 students at the Ariel School aged between six and twelve claimed that they saw one or more silver craft descend from the sky and land on a field near their school. One or more creatures dressed all in black then approached the children and telepathically communicated to them a message with an environmental theme.

The Fortean writer Jerome Clark has called the incident the “most remarkable close encounter of the third kind of the 1990s”. Skeptics have described the incident as one of mass hysteria. Not all the children at the school that day claimed that they saw something. Several of those that did maintain that their account of the incident is true.

🔗 Occupational Safety and Health 🔗 Malaysia

The Pantai Remis landslide was a rock fall and flood that occurred on 21 October 1993, near Pantai Remis in Perak, Malaysia. The landslide took place in an abandoned open cast tin mine (in a region of the state well known for its tin mining industry) close to the Strait of Malacca. Video footage shows the rapid collapse of the working face closest the sea, allowing complete flooding of the mine and forming a new cove measuring approximately 0.5 km² (0.19 sq mi).

🔗 Computing 🔗 Computing/Computer science

In computer programming, a rope, or cord, is a data structure composed of smaller strings that is used to efficiently store and manipulate a very long string. For example, a text editing program may use a rope to represent the text being edited, so that operations such as insertion, deletion, and random access can be done efficiently.

🔗 Economics

A Minsky moment is a sudden, major collapse of asset values which marks the end of the growth phase of a cycle in credit markets or business activity.

🔗 Brazil 🔗 Portugal 🔗 Catholicism 🔗 Indigenous peoples of the Americas 🔗 Brazil/History of Brazil 🔗 Spain 🔗 South America 🔗 South America/Paraguay

The Jesuit reductions were a type of settlement for indigenous people specifically in the Rio Grande do Sul area of Brazil, Paraguay and neighbouring Argentina in South America, established by the Jesuit Order early in the 17th century and wound up in the 18th century with the banning of the Jesuit order in several European countries. Subsequently, it has been called an experiment in "socialist theocracy" or a rare example of "benign colonialism".

In their newly acquired South American dominions, the Spanish and Portuguese Empires had adopted a strategy of gathering native populations into communities called "Indian reductions" (Spanish: reducciones de indios) and Portuguese: redução (plural reduções). The objectives of the reductions were to impart Christianity and European culture. Secular as well as religious authorities created "reductions".

The Jesuit reductions were Christian missions that extended successfully in an area straddling the borders of present-day Paraguay, Brazil, and Argentina (the triple frontera) amongst the Guaraní peoples. The reductions are often called collectively the Río de la Plata missions. The Jesuits attempted to create a "state within a state" in which the native peoples in the reductions, guided by the Jesuits, would remain autonomous and isolated from Spanish colonists and Spanish rule. A major factor attracting the natives to the reductions was the protection they afforded from enslavement and the forced labour of encomiendas.

Under the leadership of both the Jesuits and native caciques, the reductions achieved a high degree of autonomy within the Spanish colonial empire. With the use of native labour, the reductions became economically successful. When the incursions of Brazilian Bandeirante slave-traders threatened the existence of the reductions, Indian militias were set up, which fought effectively against the Portuguese colonists. However, directly as a result of the Suppression of the Society of Jesus in several European countries, including Spain, in 1767, the Jesuits were expelled from the Guaraní missions (and the Americas) by order of the Spanish king, Charles III. So ended the era of the Paraguayan reductions. The reasons for the expulsion related more to politics in Europe than the activities of the Jesuit missions themselves.

The Jesuit Rio de la Plata reductions reached a maximum population of 141,182 in 1732 in 30 missions in Brazil, Paraguay, and Argentina. The reductions of the Jesuit Missions of Chiquitos in eastern Bolivia reached a maximum population of 25,000 in 1766. Jesuit reductions in the Llanos de Moxos, also in Bolivia, reached a population of about 30,000 in 1720. In Chiquitos, the first reduction was founded in 1691 and in the Llanos de Moxos in 1682.

The Jesuit reductions have been lavishly praised as a "socialist utopia" and a "Christian communistic republic" as well as criticized for their "rigid, severe and meticulous regimentation" of the lives of the Indian people they ruled with a firm hand through Guaraní intermediaries.

🔗 Medicine

Pyrotherapy (artificial fever) is a method of treatment by raising the body temperature or sustaining an elevated body temperature using a fever. In general, the body temperature was maintained at 41 °C (105 °F). Many diseases were treated by this method in the first half of the 20th century. In general, it was done by exposing the patient to hot baths, warm air, or (electric) blankets. The technique reached its peak of sophistication in the early 20th century with malariotherapy, in which Plasmodium vivax, a causative agent of malaria, was allowed to infect already ill patients in order to produce intense fever for therapeutic ends. The sophistication of this approach lay in using effective anti-malarial drugs to control the P. vivax infection, while maintaining the fever it causes to the detriment of other, ongoing, and then-incurable infections present in the patient, such as late-stage syphilis. This type of pyrotherapy was most famously used by psychiatrist Julius Wagner-Jauregg, who won the Nobel Prize for Medicine in 1927 for his elaboration of the procedure in treating neurosyphilitics.

DBOS is a Database-Oriented Operating System designed to simplify and improve the scalability, security and resilience of large-scale distributed applications. It started in 2020 as a joint open source project with MIT, Stanford and Carnegie Mellon University, after a brainstorm between Michael Stonebraker and Matei Zaharia on how to scale and improve scheduling and performance of millions of Apache Spark tasks.

The basic idea is to run a multi-node multi-core, transactional, highly-available distributed database, such as VoltDB, as the only application for a microkernel, and then to implement scheduling, messaging, file systems and other operating system services on top of the database.

The architectural philosophy is described by this quote from the abstract of their initial preprint:

All operating system state should be represented uniformly as database tables, and operations on this state should be made via queries from otherwise stateless tasks. This design makes it easy to scale and evolve the OS without whole-system refactoring, inspect and debug system state, upgrade components without downtime, manage decisions using machine learning, and implement sophisticated security features.

Stonebraker claims a variety of security benefits, from a "smaller, less porous attack surface", to the ability to log and analyze how the system state changes in real-time due to the transactional nature of the OS. Recovery from a severe bug or an attack can be as simple as rolling back the database to a previous state. And since the database is already distributed, the complexity of orchestration systems like Kubernetes can be avoided.

A prototype was built with competitive performance to existing systems.

🔗 Military history 🔗 Fashion

A necktie, or simply a tie, is a long piece of cloth, worn, usually by men, for decorative purposes around the neck, resting under the shirt collar and knotted at the throat.

Variants include the ascot, bow, bolo, zipper, cravat, and knit. The modern necktie, ascot, and bow tie are descended from the cravat. Neckties are generally unsized, but may be available in a longer size. In some cultures men and boys wear neckties as part of regular office attire or formal wear. Some women wear them as well but usually not as often as men. Neckties can also be worn as part of a uniform (e.g. military, school, waitstaff), whereas some choose to wear them as everyday clothing attire. Neckties are traditionally worn with the top shirt button fastened, and the tie knot resting between the collar points.